1. Field of the Invention
The present invention relates generally to backplanes in computers.
2. Related Art
It is recognized in the art of computer systems engineering to construct a computer system as a series of printed circuit boards mounted on a backplane contained within a larger cabinet. Within the cabinet, cooling and power systems are typically provided, as well as means of connecting the computer system to other external systems.
In the computer engineering art, the backplane is known to be a hardware device that is the physical plane by which means a computer or similar device communicates with the units of which it is comprised. These units may include peripherals, memory, I/O interfaces, and central processor units. The backplane usually includes a series of connectors that are electrically connected to the internal wiring, or buses, of the computer system. Computer system units may then be attached to the computer by coupling compatible unit cards to one, or more, of the connectors on the backplane.
The use of a backplane as described above traditionally presents a number of constraints. Among the physical limitations of such an environment is the limitation on available surface area on the backplane to provide connections among the various units which may be attached to the backplane. For a system which may support a variety of unit configurations, the backplane must provide connections which may be required for each of the variety of unit configurations available for the computer system. This means that a large amount of the surface of the backplane may be consumed by providing connections which will only be used by a small subset of the possible configurations of the computer system. The addition of such connections also increases the complexity of the backplane in design and maintenance.
Even if there is sufficient surface on the backplane to provide the connections required, the sheer volume of the connections may make the resulting unit which must connect to the backplane so large as to be unwieldy and difficult to insert and remove. It may also make it necessary to provide a number of connectors to the backplane which is physically congested or undesirable due to the insertion force and removal force required for such a large number of pin connectors on the foreplane surface of the backplane.
There is also a physical limitation on the number of boards which will fit on the surface of a backplane in a given computer system. The increase in the size of a given unit board on the foreplane reduces the area available for other units.
It is often desirable to manage the connections between two or more units in the computer system as their signals pass through the backplane. However it is undesirable to provide such logic on the backplane itself because of the increase in complexity and maintenance problems associated with such a solution. That is, putting the logic functions necessary to manage communications between various unit boards on the system increases the complexity of the backplane and the cost thereof. Such a solution also increases the number of potential faults that may occur within a given backplane. If such a backplane fault occurs, the expense and difficulty of replacing the backplane is greatly increased because of the method chosen. It is therefore known to be desirable to keep the backplane design as simple as possible and to constrain complex functionality to unit boards which may be more conveniently replaced or added.